According to the development of the radio technique in recent years, a large number of techniques for estimating a position of a radio apparatus not incorporating a GPS function have been revealed. These techniques forces another radio apparatus to receive a radio wave, a communication packet, or the like transmitted from one radio apparatus, estimates a distance and a relative positional relation between the two radio apparatuses according to the strength and the direction of the received radio wave, an arrival time of the communication packet, or the like, and calculates a position of the other radio apparatus from positional information of the one radio apparatus.
These conventional techniques for estimating the position are based on the premise that the position of at least one radio apparatus has been identified. Therefore, even if a plurality of positions where a plurality of radio apparatuses are set are grasped from a working drawing or the like of a facility, when none of positions where the radio apparatuses are set is identified or when information concerning disposition is unreliable, the conventional techniques cannot be applied. In these cases, it is necessary to grasp the position of at least one radio apparatus, for example, by a visual inspection.